Refractory hollow body

ABSTRACT

The invention relates to a refractory hollow body serving especially as protection for probes or lances with which the progress of metallurgical processes is tested, to a method for producing such hollow body and to a device useful in carrying out such method. The high demands placed in such protection jacket are met by providing two layers for the refractory hollow body, i.e., an inner layer of unsintered refractory mass, containing 25 - 35 percent of fine particles and 30 - 40 percent of coarser particles, and a dense, sintered outer layer of the same material, the thickness of said outer layer amounting to preferably from one-sixth to one-tenth of the wall thickness of said body. Such jacket body, whose total porosity preferably amounts to 15 - 20 percent is produced by forming a hollow cylindrical body out of a granular, refractory mass under the addition of water and consolidation by shaking, drying said body and burning said outer layer to become dense at a temperature higher than the sintering temperature, while said inner layer is cooled by a coolant.

ited Sites Patent Truppe et a1.

[ 1 Mar. 28, 1972 [54] REFRACTORY HOLLOW BODY [72] Inventors: Meinhard Truppe; Matthias Schernthaner;

Gunter Poferl, all of Linz, Austria Primary Examiner-John J. Camby Attorney-Steinberg & Blake [57] ABSTRACT The invention relates to a refractory hollow body serving especially as protection for probes or lances with which the progress of metallurgical processes is tested, to a method for producing such hollow body and to a device useful in carrying out such method. The high demands placed in such protection jacket are met by providing two layers for the refractory hollow body, i.e., an inner layer of unsintered refractory mass, containing 25 35 percent of fine particles and 30 40 percent of coarser particles, and a dense, sintered outer layer of the same material, the thickness of said outer layer amounting to preferably from one-sixth to one-tenth of the wall thickness of said body. Such jacket body, whose total porosity preferably amounts to 15 20 percent is produced by forming a hollow cylindrical body out of a granular, refractory mass under the addition of water and consolidation by shaking, drying said body and burning said outer layer to become dense at a temperature higher than the sintering temperature, while said inner layer is cooled by a coolant.

8 Claims, 2 Drawing Figures PATENTEDmzs I972 SHEET 1 OF 2 FIE-i! PATENTEDMAR28 I972 sum 2 [1F 2 FIG. 2

REFRACTORY HOLLOW BODY The invention relates to a refractory hollow body, particularly for the protection of probes or lances such as temperature measuring lances having a cooling arrangement in their interior and destined to be immersed into hot liquid media.

In the steel industry increasing use is made of lances and the like comprising a sensing portion which is entirely or partly cooled, which lances are immersed into hot metal baths in order to observe the progress of metallurgical processes. Devices of this kind are e.g. temperature measuring lances, in the sensing portion of which a thermocouple with a sheath tube is encased. The sheath tube with the thermocouple has to be protected against the influence of slag and metal by means of a refractory jacket; when such temperature measuring devices are employed e.g. in top blowing converters it is desired that the life of the device lasts for a larger number of heats. The refractory protection jacket is required to be resistant against the specific thermal stresses which arise from the great temperature gradient from the hot outside to the interior which is entirely or partly cooled; to be resistant against the chemical attack of liquid slag and metal; and to show firstrate fireproof properties as well as a good resistance to thermal shocks. Owing to the described temperature difference between the outside and the interior and to the relatively small wall thickness which such ajacket may have, the relevant temperature gradient is much greater than that which may occur in refractory bricks used for lining an open-hearth furnace or a converter; a stationary distribution of temperature cannot occur because the measuring lance remains but shortly in the bath, e.g. for 20-25 minutes during a refining heat, after which the measuring lance is drawn out again. It will therefore be understood that the demands placed in the refractory jacket of the sensing portion of a lance are immensely greater than those placed in e.g. roof bricks subjected to the highest stresses. Until now it has not been possible to achieve a satisfactory life and resistance of protection jackets for measuring lances. Burnt basic stones, though chemically adequately resistant, cannot cope with the sudden change of temperature when they are immersed into the hot metal baths and fail to withstand the great temperature gradient; they are liable to cracks and burst off. Graphite bricks which stand out for their resistance to thermal shocks likewise have not proved satisfactory because the liquid steel chemically affects the graphite material. lt has not been possible so far to extend the life of the protection jacket over a plurality of heats.

The present invention is aimed at avoiding the drawbacks and difficulties described by creating a refractory hollow body, particularly for the protection of probes or lances, such as temperature measuring lances having a cooling arrangement in their interior and destined to be immersed into hot liquid media, which is characterized in that the hollow body comprises an inner layer of unsintered refractory mass and a dense, sintered outer layer of the same material.

The dense outer layer of the hollow body according to the invention is resistant against chemical and mechanical corrosion by liquid slag and liquid steel up to temperatures of about 1,700" C. and even more. The inner layer which is unsintered and carries the outer layer is deformable and therefore may follow heat tensions which occur as a result of temperature fluctuation stresses. Owing to this deformability the occurrence of cracks is avoided. With the hollow body according to the invention the life of the lance lasts for a plurality of refining heats, e.g. more than 10.

A certain ratio is to be maintained between the thickness of the sintered outer layer and the wall-thickness of the inner layer. The inner layer at any rate has to be considerably thicker than the outer layer. Preferably the thickness of the sintered outer layer amounts to one-fourth or less of the wall thickness of the entire hollow body, especially one-sixthonetenth of the wall thickness. ln this connection it is essential that the inner layer has a certain degree of porosity for only then it remains deformable and, so to speak, suitable as an elastic carrier for the dense outer layer. The best results are obtained when the total porosity of the hollow body amounts to -20 percent.

The invention further comprises a process for the production of the described hollow body, which process resides in that a hollow cylindrical moulded body is formed out of a granular, refractory material under addition of water and consolidation by shaking, which body is dried and its outer layer is burnt to become dense at a temperature higher than the sintering temperature while its inner layer is cooled by a coolant. Preferably the body is dried in two steps, namely by air-drying at room temperature and subsequent drying at increased temperature in the range of 200 to 650 C, preferably 400-450 C. Reinforcement rods, wires or nets may be incorporated into the body in the mould.

Further, the granulation of the material from which the hollow body is produced is important: The refractory mass should contain 25-35 percent of fine particles having a grain size of up to 0.10 mm. and 30-40 percent of coarser particles having a grain size of 2.5-5 mm.

The hollow body according to the invention and the process for its production or a device for carrying out the process, respectively, are illustrated in the drawings. FIG. 1 is a vertical longitudinal section through the refractory hollow body according to the invention receiving the sensing portion of a temperature measuring lance. In FIG. 2 a device for producing a hollow body is shown.

The hollow body 1 according to the invention is provided with a central bore which is enlarged approximately in the upper third, i.e. it has a greater diameter there, to receive the probe head 11. The probe comprises three concentrical tubes 7, 8 and 9; the compensating line, namely two conductors encased in a sleeve 10, being arranged in the inner tube 7, said conductors serving for the connection to the outside of the thermocouple limbs situated in the sensing portion of the apparatus. The tube 8 ends short of the probe head. It represents a guide tube for the formation of a coolant circulation. The sensing portion which is connectable with the probe head is generally denoted by numeral 12 in FIG. 1. It comprises a sheath tube 13, in which the thermocouple 14 with its hot juncture 15 is encased, and the hollow body 1 according to the invention which surrounds the sheath tube and, when the measuring lance is inserted into the bath, comes to lie in the area of the slag layer 3 floating on the bath 2. In this region of the slag layer the greatest stresses occur, as is well known. The tip 4 of the sensing portion in which the hot juncture is situated projects from the hollow body 1 in downward direction.

As may be derived from the drawing, the hollow body 1 comprises an inner layer 5 consisting of unsintered, refractory granulated mass, and a dense, sintered outer layer 6 consisting of the same material. A basic ramming mass of preferably the following composition is suitable as refractory mass:

4.0 6.0% mo, s3 88% M go 2 3% CaO 0.4 0.6% sio, 3.5 3.7% Auo,

about 1.20% loss at red heat, whose sieve analysis is the following:

less than 0.05 mm. 20.88%

0.05 0.10 mrnv 7.90%

more than 5.00 mm. 0.52%. The apparent weight of such a mass amounts to e.g. 1.85 gJcm".

The hollow body is produced in that after the addition of 5-7 percent by weight of water the mass is filled into a mould under slight shaking where it is consolidated by further, stronger shaking. In the mould a reinforcement body made of steel wire may be inserted. The hollow body is then predried at room temperature for 24 hours in the mould and for 48 hours outside the mould. At temperatures of about 450 C. it is further dried for about 48 hours during which the hollow body is suspended in the kiln. After these two drying steps the hollow body shows the following characteristics:

volumetric weight average 2.848 gJcmi s ecific weight average 3320 gJcm. total porosity average 14.22% open porosity average I l.02%.

The dense sintered outer layer is produced by burning the hollow body at a temperature of about l,600 C. for about 2 hours. For this purpose the device according to FIG. 2 may be used. The predried hollow body 1 is suspended on a watercooled carrier 16, whose shape corresponds to the inner contour of the hollow body, and is inserted into the burning chamber 17 ofa kiln 18. The burning chamber is covered by a lid 19. Arrows indicate the supply and draining of water. While the outer layer is sintered, the inner part of the hollow body is continuously cooled. Instead of water also air may be used as coolant. The total wall thickness of a hollow body produced according to the invention may amount to e.g. 60 mm., the thickness of the sintered outer layer amounting to about mm.

Hollow bodies according to the invention have proved highly satisfactory in practice. When used in top blowing oxygen converters service periods lasting for more than ten charges have been achieved without difficulties, the measuring lance having been in use for the overall blowing period and exposed to cooling off by air in the intervals between blowing, which meets the severest conditions that may occur in a steelmaking plant. If, instead of exposing it to cooling off by air in the intervals between blowing, the measuring lance is brought into a warming chamber kept at a temperature of about l,00O C., the life of the hollow body according to the invention will be considerably increased, so that it will last e.g. for more than 20 charges.

We claim:

1. A refractory hollow body for the protection of heat-sensitive instruments against severe thermal stresses comprising an inner layer of unsintered refractory mass and a dense, sintered outer layer of the same material, said body being composed throughout said inner and outer layers of a packed mass of granular refractory material all of which is capable of being sintered but which has only said outer layer thereof sintered with said outer layer merging into and carried by said inner layer, the latter being substantially thicker than said outer layer and having a degree of porosity greater than said outer layer.

2. The refractory hollow body set forth in claim 1, wherein said hollow body has an exposed outer surface formed in its entirety by said outer layer and said body being formed with a bore which defines the hollow interior of said body, said bore having a pair of opposed end regions where said outer layer is located and being defined between said end regions by a surface of said inner layer.

3. The refractory hollow body set forth in claim 2 and wherein said bore extends completely through said body for accommodating an instrument which extends sufficient to extend through and beyond a layer of slag on the molten metal so that an instrument extending through said bore is protected by said body from the slag.

4. The refractory hollow body set forth in claim 1, wherein said inner layer of unsintered refractory mass contains 25-35 percent of fine particles having a grain size of up to 0. l0 mm. and 30-40 percent of coarser particles with a grain size of 2.5 to 5 mm. 7

5. The refractory hollow body set forth in claim 1, wherein the maximum thickness of the sintered outer layer amounts to one-fourth of the wall thickness of the entire hollow body.

6. The refractory hollow body set forth in claim 1, wherein the thickness of the sintered outer layer is between one-sixth and one-tenth of the wall thickness of the entire hollow body.

7. The refractory hollow body set forth in claim 1, wherein the total porosity of said hollow body amounts to 15-20 percent.

8. The hollow body set forth in claim 1 which is adapted for protectively encasing an internally cooled, thermocouple-type temperature measuring lance destined to be immersed into hot liquid media.

316520068 Dated March 8' Patent No.

Inventor s) Meinhard Truppe et a]. 0

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 18, between "extends" and "sufficient" insert--through and beyond said bore and said body,

and said body having a height="-o Signed and sealed this 22nd day of Axigust 1972 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1 (10-69) uscoMM-oc eoavs-peg U. 5 GOVERNMENT PRINTING OFFICE: I969 0-466-33 Patent No.

Invehtor(s) Meinhard Truppe, et a]...

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4,, line 18, between "extends" and "sufficient" insert--through and beyond said bore and said body,

and said body having a heig1nt----a Signed and sealed this 22nd day of August 197.2u

(SEAL) Attest:

EDWARD M.FLETCHER,JR.. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10 69) uscoMM-Dc eo U.5 GOVERNMENT PRINTING OFFICE: I969 O-366-334 

2. The refractory hollow body set forth in claim 1, wherein said hollow body has an exposed outer surface formed in its entirety by said outer layer and said body being formed with a bore which defines the hollow interior of said body, said bore having a pair of opposed end regions where said outer layer is located and being defined between said end regions by a surface of said inner layer.
 3. The refractory hollow body set forth in claim 2 and wherein said bore extends completely through said body for accommodating an instrument which extends through and beyond said bore and said body, sufficient to extend through and beyond a layer of slag on the molten metal so that an instrument extending through said bore is protected by said body from the slag.
 4. The refractory hollow body set forth in claim 1, wherein said inner layer of unsintered refractory mass contains 25-35 percent of fine particles having a grain size of up to 0.10 mm. and 30-40 percent of coarser particles with a grain size of 2.5 to 5 mm.
 5. The refractory hollow body set forth in claim 1, wherein the maximum thickness of the sintered outer layer amounts to one-fourth of the wall thickness of the entire hollow body.
 6. The refractory hollow body set forth in claim 1, wherein the thickness of the sintered outer layer is between one-sixth and one-tenth of the wall thickness of the entire hollow body.
 7. The refractory hollow body set forth in claim 1, wherein the total porosity of said hollow body amounts to 15-20 percent.
 8. The hollow body set forth in claim 1 which is adapted for protectively encasing an internally cooled, thermocouple-type temperature measuring lance destined to be immersed into hot liquid media. 